driven by an electric motor. A standard platinum resistance 

 thermometer and a temperature sensing quartz probe pene- 

 trate an aperture in the lid (fig. 2). Another hole provides 

 for the entry of electrical leads for connection to any 

 electronic equipment being calibrated. A motor and 

 accessory drive, situated on the right side, are used to 

 rotate the thermometer rack through 180° in a vertical 

 plane while the lid is closed. Another motor, centrally 

 located on top of the lid, drives a system of gears and cams 

 (known as a Geneva movement) (fig. 2) which, alternately, 

 advances and holds the rack stationary, to enable the 

 thermometers to be read successively at the telescope. 

 This is the indexing system. Indexing time between ther- 

 mometers is 7 seconds. 



Two shock-mounted 1/10-hp stirring motors, 

 connected by rubber driving belts to two stirring shafts, 

 are installed on the tank lid. The V-belts formerly used 

 to drive the stirring propellers were irregular in thickness 

 and caused vibration which was transmitted through the lid 

 to the thermometer rack, making the etchings and meniscus 

 of the thermometers appear blurred. This problem was 

 solved by substituting flat, geared, timing belts of uniform 

 cross section throughout their length for the V-belts. A 

 stainless-steel, four-bladed propeller is mounted on each 

 stirring shaft at diagonal corners of the lid (fig. 4a, page 11). 

 The thrust of one is up and of the other down, to impart a 

 vertical rotary motion to the water for thorough mixing. 



A problem was encountered when the Oilite 

 bronze propeller-shaft bearings wore rapidly below the 

 waterline, Nylatron, a graphite-impregnated Nylon, was 

 tried as a bearing material but it swelled in water and 

 seized the shafts. Teflon was also tried but it too caused 

 seizure. In addition, the downward pull of the right-hand 

 propeller plus the weight of its shaft caused the thrust 

 face of the bearing to flake, and rapid wear occurred. This 

 problem did not appear in the left-hand bearings because 

 here thrust is down, offsetting the weight of the shaft. The 

 problem was solved by using a composite bearing composed 

 of Type 316 stainless-steel balls carried in a Nylon retainer 

 and running in Delrin inner and outer races. =■= 



*No. 21462-9 Type A, General Bearing Co., West Nyack, New York 



